The present invention relates to gait modulation systems and methods therefor, and more particularly, to a functional electrical stimulation (FES) orthosis device and a sensor device for such gait modulation systems, and to method of using such devices.
It is known that pathologies of the neuromuscular system due to disease or trauma to the central nervous system, such as stroke, spinal cord injury, head injury, cerebral palsy and multiple sclerosis, can impede proper limb functioning of the hands or legs. Gait, the biomechanical description of walking, can suffer static and dynamic parameter variations due to neuromuscular impairments, which cause non-symmetrical walking, reduced walking speed and reduced walking stability.
Drop foot describes the gait attributable to weak or uncoordinated activation of the ankle dorsi-flexors due to disease or trauma to the central nervous system. Patients suffering from drop foot tend to drag the foot during the swing phase of walking and usually try to compensate for this dragging by hiking their hip or swinging it in a circular motion. These patients tend to have impaired stability, are prone to frequent falls, and their walking movements are unaesthetic and energy consuming.
However, limb muscles can generally be activated with FES. In FES, precisely timed bursts of short electrical pulses are applied to motor nerves, to generate muscle contraction, which can be applied to enhancing limb function.
Although more than four decades have elapsed since the first neuroprosthetic system was proposed, much room remains for improving the technological quality of such systems. This is reflected, inter alia, by the relatively small percentage of potential users who regularly don a neuroprosthetic device to compensate for limb and gait problems, and particularly, a drop foot problem. These systems suffer from many drawbacks that prevent them from being widely used by potential patients.
When problems with arm movement or gait result from stroke or brain injury, they are often accompanied by hand impairment on the same side of the body as the limb on which the FES orthosis is donned. Thus, the donning action must often be carried out using solely the contra-lateral, unaffected hand. Moreover, the posture of the plegic limb is often problematic, especially in cases where spasticity results in reduced voluntary movements and also in a limited passive range of motion of the limb joints. Consequently, objective biomechanical problems exist in donning the orthotic device and in locating the electrodes in exact position onto the limb. Prior art neuroprosthetic devices differ in that they fail to enable facile, quick and accurate donning of the device by an impaired patient using a single hand, and particularly, when even that hand is shaky or otherwise unstable.
Prior art external FES devices typically utilize a stimulator unit that is physically separate from the FES orthosis, to create and control the electrical pulses being applied to motor nerves. The external stimulator unit, which is connected to the FES electrodes by several electrical wires, is located on the body of the user, and is typically attached to the belt of the user. These devices can be inconvenient for the user. Particularly cumbersome is the wiring, which is usually arranged to run along the leg under the clothing to connect the device components.
In addition, neuroprostheses require precise fitting for each individual patient, in an optimal fashion, by exactly identifying the stimulation points that cause contraction of the muscles and positioning and locking the electrodes thereto. Consequently, use of the known devices, which are configured and dedicated to the anatomy and needs of a particular individual, is limited to that individual only, and further requires considerable expertise to reconfigure the device for transfer to another patient.
U.S. Pat. Nos. 5,643,332 and 5,814,093 to Stein disclose an assembly for functional electrical stimulation during movement, including a band, mountable on the leg, carrying all of the components of the assembly to provide a self-contained unit. The components include: electrodes for stimulating a leg nerve; a V-shaped plate for conforming with the leg's tibia to reproducibly position the band so that the electrodes are located over the nerve; a tilt sensor for measuring the angular position of the lower leg; a control circuit for processing the sensor signal information and emitting pulses through the electrodes to stimulate the leg in response to phases of body movement and a battery for supplying power to the tilt sensor, control circuit and stimulator. The disclosed band is made of stretchable, breathable material.
WalkAide™ is a commercially available FES device of Innovative Neurotronics, Inc., and is based on the technology disclosed by Stein. The orthosis component of the WalkAide™ is a narrow band made of a thermoplastic material that is molded to the limb anatomy of an individual user by heating and softening the thermoplastic material and subsequently fitting the contour to the contour of the underlying limb segment. Thus the shape and size of the device and the electrode positioning is custom-fitted to the leg of one user and individualized for the user. This procedure is carried out by a trained medical professional.
For a clinic or rehabilitation center serving a large number of users, it would be advantageous a device that can be transferred from patient to patient hygienically and with facility. Neuroprosthetic devices require a significant and time-consuming set-up procedure carried out by a trained medical professional to fit the device to the anatomy of the limb, position the electrodes accurately over the motor point, and adjust the stimulation parameters when transferring the device to another patient. Parts of the orthosis are in prolonged contact with the skin during a session of use, and existing devices have no provision for hygienically passing the orthosis from the leg of one patient on to another.
Prior art orthosis-based devices for the leg such as the WalkAide™ device operate with relatively small electrodes typically having a diameter of 25-30 mm and a surface area in contact with the skin of no more than about 5-7 cm2 positioned relatively close together in the orthosis. This enables the orthosis to take the form of a relatively narrow band to accommodate the small electrodes and separation. However, activation of the leg muscles by electrical stimulation requires typically high stimulation currents. But the stimulation current passing through the electrode to the skin surface activates skin sensory receptors in addition to underlying excitable motor nerve and muscle tissue and the intensity of sensory activation will depend on the intensity of the current density passing through the skin surface. The level of muscle activation is often limited in the typical patient by his individual tolerance to activation of these skin pain sensors. For these patients, it would be advantageous to reduce the sensory discomfort by lowering the skin current density while maintaining levels of muscle activation. A further means to increase the contraction force of the activated muscles is to increase the distance separating the electrodes in the pair, particularly the distance along the length of the leg. This can result in the recruitment of more muscle fibers, resulting in increased activated rotation torque output from the ankle joint, without the necessity to use a high stimulation current intensity. This electrode geometry and arrangement for increasing muscle force output and reducing sensory discomfort is too large to fit within the prior art narrow band design of the orthosis. To date, no orthosis exists for accommodating surface electrodes of such size and configuration.
Furthermore, a means for accurately positioning the electrodes along the length of the leg becomes essential where the electrodes are significantly separated in this longitudinal direction, and accurate longitudinal positioning of the orthosis becomes mandatory to avoid activating unwanted muscles. Accommodating the large stimulation electrodes with a larger distance separating them particularly in the longitudinal direction requires housing these electrodes in an orthosis that is significantly wider, extending both proximally and distally along the length of the leg. The wide orthosis design introduces new problems concerned with fitting and self-placement. Moreover, the larger dimensions of the orthosis appreciably compromise the ability of the orthosis to fit the contour of the limb segment, especially during limb extensions, flexions and gait.
Some commercially available FES devices utilize a sensor, for disposing underneath the foot of the user, to trigger the electrical pulses being applied to the motor nerves. The sensor senses foot rise or foot strike and accordingly triggers the stimulation pulses administered to the motor nerves. The sensor device is physically distinct from the orthosis.
U.S. Pat. No. 6,507,757 to Swain, et al., discloses one typical foot sensor device of the prior art, in which a foot pressure switch, or sensor, is permanently disposed in the shoe of the affected leg. An electrical circuit is interrupted during the stance phase, when a significant weight is placed on the heel, and reconnects when the heel is lifted during the swing phase. Wires disposed under the clothing connect the sensor with an external stimulator unit that can be attached to the belt or kept in a pocket of the user. The stimulator unit is connected to the electrodes by additional electrical wires.
In other FES orthotic devices, the cumbersome wires are obviated by using a radio frequency (RF) system in which the foot sensor device and other components of the FES orthotic device communicate in a wireless fashion. How-ever, the use of such an RF system necessitates integrating an RF transmitting unit, or head, within the foot sensor device. The transmitting unit can be bulky and sensitive to humidity and mechanical stress. Consequently, such transmitting units are typically mounted on and attached to the calf of the patient.
U.S. Pat. No. D494,273 to Haugland, et al., assigned to Neurodan A/S, describes a pressure sensor switch device for placing underneath the foot of the patient. The communication head is held at a predetermined distance from the sensor device by a wide, semi-rigid spine. The device disclosed by Haugland, et al., can be used as a component of the ActiGait® system manufactured by Neurodan A/S. In the ActiGait® system, the pressure sensor device is inserted into a small pouch within a sock, such that upon donning of the sock, the pressure switch is disposed underneath the foot. A substantially non-elastic band is tightened around the calf to secure the RF unit in place against the calf of the impaired leg.
This approach is disadvantageous in that the patient, who is often hemi-plegic or may suffer from other disorders, is required to add the donning of an additional item the sock to his routine. This unintuitive action is particularly problematic for patients who need or prefer to don the FES orthotic device in an unassisted fashion.
A further disadvantage of this design is that the semi-rigid spine may rub against the foot and heel. Also, the electronic head that houses the RF transceiving unit may rub the ankle or lower calf of the user during the course of gait. Moreover, because the pressure switch and RF transceiving unit are mechanically connected by a wide, at least semi-rigid neck, pressures exerted on the electronic head (e.g., when the head gets caught on, or bumped by, an object during the course of gait), are mechanically translated into forces on the foot sensor. These forces may impede the efficacy and sensitivity of the foot sensor. A further disadvantage lies in the limited ability to adjust the electronic head of the pressure switch to different shoe heights: the electronic head protrudes excessively from low-rimmed shoes, and cannot be fitted to shoes or boots in which the rim is at or above the height of the electronic head.
There is therefore a recognized need for, and it would be highly advantageous to have, a sensor device for neuroprosthetic gait enhancement that overcomes the various deficiencies of the prior art devices. It would be of particular advantage to have such a sensor device that is essentially effortless to don, avoids the discomfort associated with prior art sensor devices, and is secured so as to operate in a safe and robust fashion.
It would also be highly advantageous to have an improved FES orthosis for a neuroprosthetic system and method that overcome the manifest deficiencies of the prior art. It would be advantageous to have an FES leg orthosis that can easily and accurately be donned on the limb by patients also suffering from an impaired hand. It would also be of particular advantage to have an FES leg orthosis in which an even pressure of the electrode surface is maintained during limb extensions, flexions and gait. It would be of further advantage to enable greater ankle torque generation with lessening of skin sensory discomfort at the electrode site by increasing the size and longitudinal separation of the electrodes. It would be of yet further advantage for the FES orthosis to be substantially universally adaptable to the different anthropometric variables of limbs and to electrode positioning needs of a wide variety of users. Finally, it would be advantageous to have an FES orthosis designed and configured such that the on-board stimulation unit does not significantly protrude outside the profile of the orthosis and does not impede donning and wearing clothing such as trousers over the orthosis. This is of major significance to the stroke patient, who is generally is challenged by donning trousers on to his plegic leg using a single hand, and a protruding device attached to his leg may disable his ability to dress himself independently.